Electrically insulating carrier particles

ABSTRACT

Carrier particles useful in developing electrostatic charge patterns are provided with a thin layer in insulating material by glow discharge treatment.

Unite States Patent Wright et a1. June 13, 1972 [54] ELECTRICALLYINSULATING 3,387,991 6/1968 Erchak ..1 17/93.l CARRIER PARTICLES3,247,014 4/1966 Goldberger et a1. ..1 17/100 3,447,950 6/ 1 969 Evanset a1 ..1 17/ l 00 1 Inventors: J g Bruce J- Rubin, both of 3,526,5339/1970 Jacknow et a1. ..117/100 Rochester, 3,440,085 4/1969 Baker et a1...117 100 [73] Assigneez Eastman Kodak Company Rochester, 3,461,0928/1969 Stony ..260/28 3,392,139 7/1968 Dingman ..260/41 3,533,82910/1970 Quanquin 117/6212 [22] Filed: Feb. 3, 1970 3,326,177 6/1967Taylor ..118/49 1 [21] APPLNO; 3,416 3,466,191 9/1969 Stinchfield et a1...117/213 Primary Examiner-George F. Lesmes [52] US. Cl. ..252/62.1, ll7/93.1 R, l 17/93.1 GD, Assistant E i h C Cooper, [[1

117/931 CD, 117/175, 1 17/100 C, 117/10 M, Attorney-W. H. J. Kline, J.R. Frederick and T. Hiatt ll7/D1G. 6, 117/D1G. 8, 204/168 [51] Int. Cl...G03g 9/00 7 ABSTRACT [58] Field of Search ..252/62.1; 117/93] R, 93.1GD,

1 17/93.1 CD, 100 C, 100 M, 17.5, DIG. 6, DIG. 8; Carrier particlesuseful in developing electrostatic charge pat- 204/168 terns areprovided with a thin layer in insulating material by glow dischargetreatment. 56 R f C'ted 1 e erences l 6 Claims, No Drawings UNITEDSTATES PATENTS 3,507,686 4/1970 Hogenboch ..117/100 ELECTRICALLYINSULATING CARRIER PARTICLES This invention relates toelectrophotography, and more particularly, to magnetically attractablecarrier particles useful in the magnetic brush type development ofelectrostatic images.

Electrophotographic imaging processes and techniques have beenextensively described in both the patent and other literature, forexample, US. Pat. Nos. 2,221,776; 2,277,013; 2,297,691; 2,357,809;2,551,582; 2,825,814; 2,833,658; 3,220,324; 3,220,831; 3,220,833 andmany others. Generally, these processes have in common the steps ofemploying a normally insulating photoconductive element which isprepared to respond to imagewise exposure with electromagnetic radiationby forming an electrostatic charge image. The electrostatic latent imageis then rendered visible by a development step in which the chargedsurface of the photoconductive element is brought into contact with asuitable developer mix.

One method for applying the developer mix is by the wellknown magneticbrush process. Such a process generally utilizes apparatus of the typedescribed, for example, in U.S. Pat. No. 3,003,462 and customarilycomprises a nonmagnetic rotatably mounted cylinder having fixed magneticmeans mounted inside. The cylinder is arranged to rotate so that part ofthe surface is immersed in or otherwise contacted with a supply ofdeveloper mix. The granular mass comprising the developer mix ismagnetically attracted to the surface of the cylinder. As the developermix comes within the influence of the field generated by the magneticmeans within the cylinder, the particles thereof arrange themselves inbristle-like formations resembling a brush. The bristle formations ofdeveloper mix tend to conform to the lines of magnetic flux, standingerect in the vicinity of the poles and lying substantially flat whensaid mix is outside the environment of the magnetic poles. Within onerevolution the continually rotating tube picks up developer mix from asupply source and returns part or all of this material to the supply.This mode of operation assures that fresh mix is always available to thesurface of the photoconductive element at its point of contact with thebrush. In a typical rotational cycle, the roller performs the successivesteps of developer mix pickup, brush formation, brush contact with thephotoconductive element, brush collapse and finally mix release.

In magnetic brush development of electrostatic images the developer iscommonly a triboelectric mixture of fine toner powder comprised of dyedor pigmented thermoplastic resin with coarser carrier particles of asoft magnetic material such as ground chemical iron (iron filings),reduced iron oxide particles, or the like.

The relatively high conductivity of iron and similar ferromagneticcarrier particles can be useful in magnetic brush development in that aconducting magnetic brush serves effectively as a development electrode,and as a consequence, the fringing field created by an electrostaticlatent image is modified and solid area development is achieved.However, solid area development by such a means has the disadvantage ofvery narrow exposure latitude and hence conducting carriers are to beavoided if one desires to take advantage of fringing field effects toincrease exposure latitude. Accordingly, there is a need for a magneticbrush developing composition which is capable of producing good imageswithin a wide range of exposure latitude.

Resinous coatings on iron or other magnetic brush carrier granules canincrease the surface resistance and the tendency toward fringingdevelopment. However, application of a coating of insulating resin ofsufficient minimum thickness to effect the required reduction in surfaceconductivity is a difficult operation. The plastic, whether applied froma melt, a hydrosol, or a dope, tends to solidify to a compact mass withthe carrier particles, so that it is difficult to recover the coatediron in the desired form of discrete uniformly coated bits. Grinding orother forms of comminution of such a compacted or agglomerated mass ofparticles will usually result in exposing a sufficient amount of theconducting surface of the underlying particles to largely negate theintended improvement in resistance. Thus, prior coating proceduresinvolve multi-step processes which make it difficult to control thethickness of the material deposited on the underlying core and whichgenerally do not result in a continuous film being formed on eachindividual particle. A further problem with prior coating techniques isthat the outer layer of coated material is generally subject to wearduring usage which results in a variation in the physical propertieswith time.

Accordingly, there is a need for improved carrier materials having acontinuous film of controlled thickness of insulating material which isabrasion resistant. There is likewise a need for a simple process forforming a continuous film of insulating material on carrier particleswhich film is not subject to wear and which process can readily becontrolled.

It is, therefore, an object of this invention to provide a novel methodof preparing carrier particles having a continuous uniform electricallyinsulating polymeric coating thereon.

It is another object of this invention to provide novel carriermaterials having a high electric resistance.

An additional object of this invention is to provide novel carrierparticles which have an outer polymeric coating which is resistant towear.

It is a further object of this invention to provide magneticallyresponsive carrier particles having a thin, continuous layer of polymercoated thereon and which particles are useful in the development ofelectrostatic charge patterns.

Still another object of the invention is to provide new developercompositions suitable for use in fringing development of electrostaticlatent images.

These and other objects and advantages are accomplished in accordancewith this invention by the preparation and use of improved carrierparticles having a relatively high electrical resistance. Theseparticles are each comprised of a core material of appropriate size andshape over which is coated athin, continuous layer of electricallyinsulating resinous material.

The core materials which can suitably be overcoated in accordance withthis invention include a variety of materials such as magnetic andnonmagnetic materials. Typical nonmagnetic materials include, forexample, glass beads or crystals or organic salts such as sodium orpotassium chloride. The present invention is particularly well suitedfor use with cores of magnetic materials. The phrase "magneticmaterials" as used herein encompasses a variety of magneticallyattractable materials. Particularly useful materials wouldincludeferromagnetic materials such as metals of the first transition series,i.e., nickel, iron, cobalt, and alloys containing any or all of thesemetals. Other useful materials which exhibit a net magnetic moment arethe ferrimagnetic materials. Examples of such ferrimagnetic materialswould include the ferrites, which are materials having the generalformula Meo-Fe O where Me is a metal ion, as well as the mixed ferrites,which contain more than one species of metal ion in addition to iron,and the substituted ferrites, in which another metal replaces some ofthe iron. Also included in the phrase magnetic material are particlessuch as those described in copending Miller U. S. application Ser. No.562,497, filed July 5, 1966, now abandoned, entitled ELECTROPHOTOGRAPHICDEVELOPING COMPOSITIONS, and which are comprised of, for example, irondispersed in a resin binder. Such magnetic materials are used as a corein accordance with this invention over which is coated a film-formingresinous material. The core can consist of a solid particle of magneticmaterial or can be a nonmagnetic particle overcoated with ferromagneticmaterials as described in copending Miller U. S. application Ser. No.699,030, filed Jan. 19, 1968, now abandoned, entitled METAL SHELLCARRIER PARTICLES.

The core material used, whether magnetic or nonmagnetic, can vary insize and shape, with core materials having an average diameter of fromabout 1,200 to about 30 microns being useful. Particularly usefulresults are obtained with core materials of from about 600 to about 40microns average diameter. The size of the core particles used, will, ofcourse,

depend upon several factors such as the type of image ultimatelydeveloped, desired thickness of the polymeric coating, etc. The phraseaverage diameter" as used herein is not meant to imply that onlyperfectly uniformly dimensioned particles can be used. This phrase isused to refer to the average thickness of particles when measured alongseveral axes. Average diameter also refers to the approximate size ofthe openings in a standard sieve series which will just retain or justpass a given particle.

In accordance with this invention, the core particles are coated with acontinuous film of resinous material. A thin layer of material isapplied to the core particles by a procedure which we generally refer toas glow discharge polymerization." In glow discharge polymerization, anorganic vapor at about 0.5 to 5.0 mm. of mercury pressure is introducedinto a chamber containing two parallel closely spaced electrodes. Whena.c. or d.c. fields of the order of several hundred v/crn. are imposedon the parallel electrodes, a uniform discharge forms between the platesand polymeric films are deposited on articles contained between theelectrodes. in general, this procedure involves introducing aconcentration of a vaporous or gaseous monomer or other polymerprecursor into a reaction chamber containing suitable core particles andsubjecting the materials to activating electromagnetic radiation tocause the monomer or polymer precursor to undergo polymerization on thesurface of the core particles. During this procedure, the particles arekept in motion by any suitable means. The apparatus involved in formingthese thin polymer layers is quite simple, and is mainly comprised of achamber which may be evacuated to a pressure of the order of about 0.1to about 3 mm. of mercury. After evacuating the chamber, an unreactivegas such as helium is bled into the apparatus to increase the pressureto about 0.3 to 5 mm. of mercury. Within this chamber is located a meansfor containing and vibrating or otherwise thoroughly agitating the coreparticles to be coated. One suitable means for this purpose is analuminum plate which is maintained at ground potential and which is heldin an insulating holder that is capable of being vibrated so as tomaintain the particles in a relatively fluidized state. Located abovethe plate holding the particles is a large high potential electrodetypically prepared of stainless steel. This electrode is maintained inclose proximity to the particles, usually at a distance of about 1% toabout 2% cm. depending on the potential applied, etc. This electrode isconnected to a power source capable of maintaining at least a kilocyclea.c. field sufficient to produce an even glow. Of course, glow dischargeis typical of many suitable arrangements which can be used to activatethe vaporized monomer. Other useful means of activation would includedirect current, electrodeless radio frequency, microwave glow discharge,as well as ultraviolet radiation and electron bombardment.

Prior to forming a polymer coating on the core particles, it is oftendesirable to clean the particles. This can be done by introducing heliumor other nonreactive gas into the system and subjecting the particles toglow discharge treatment. The helium is bled off and then the vaporizedmonomer or polymer precursor is introduced into the chamber at apressure of 0.5 to 5 mm. of mercury and once again subjected to a glowdischarge. The vaporizable monomer or polymer precursors which areuseful can be selected from a wide variety of materials. Suitablematerials would include such monomers as trifluoromonochloroethylene,hexafluoropropylene, tetrafluoroethylene, octafluorobutene-Z, vinylfluoride, vinylidene fluoride, hexafluoroacetone, acrylonitrile,styrene, ethylene, vinyl chloride, vinyl ferrocene, methyl methacrylate,divinylbenzene, carbon tetrachloride, hexafluoroethane, etc, as well asmaterials which are not generally considered as polymer precursors suchas benzene, naphthalene and anthracene. In general, any vaporizablevinyl monomer is suitable for use herein. In addition, mixtures of theseor any other vaporizable polymer precursors which undergo polymerizationin the presence of activating radiation can be used.

in accordance with the present techniques, extremely thin, continuouslayers of electrically insulating materials can be applied to variouscore materials. In general, the amount of resin applied is usually inthe range of from about 0.003 to about 4 percent by weight of the corematerial being coated with preferred materials having a resin coating offrom about 0.03 to about 0.2 percent by weight of the core. The averagethickness of the continuous film of polymer applied in accordance withthis technique is in the range of from about 0.005 to about 4.0 microns,with a thickness of about 0.05 to about 0.2 microns being preferred.

Typically, the electrical resistance of the coated carrier particles ofthis invention is greater than about 10' ohms with preferred carriershaving a resistance of greater than about 10 ohms. Generally, it can besaid that the higher the resistance of the carrier particle, the betterthe quality of the fringe development obtained. Of course, aboveextremely high levels of resistance the increase in quality of fringedevelop ment per unit increase of resistance becomes so small as to benegligible. For purposes of comparison, the resistance of variousmagnetically attractable carrier particles is measured in a standardmagnetic brush resistance test. This test is conducted each time using a15 gram quantity of the carrier particles. A cylindrically shaped barmagnet having a circular end of about 6.25 cm. in area is used toattract the carrier and hold it in the form of a brush. After formationof the brush, the bar magnet is then positioned with the brush-carryingend approximately parallel to and about 0.5 cm. from a burnished copperplate. The resistance of the particles in the magnetic brush is thenmeasured between the magnet and the copper plate.

The resin layers formed on the carrier particles of the presentinvention are extremely durable and abrasion resistant. The improvedabrasion resistance of the present polymer coatings appears to be aresult of the considerable crosslinking which occurs during thedischarge polymerization reaction used to coat the core materials.

Electroscopic developer compositions can be prepared by mixing fromabout to about 99 percent by weight of the present carrier particleswith from about 10 to about 1 percent by weight of a suitableelectroscopic toner material. The toner granules useful with the carrierare generally comprised of a resin binder and a colorant. Suitabletoners can be selected from a wide variety of materials to give desiredphysical properties to the developed image and the proper triboelectricrelationship to match the carrier particles used. Generally, any of thetoner powders known in the art are suitable for mixing with the carrierparticles of this invention to form a developer composition. When thetoner powder selected is utilized with ferromagnetic carrier particlesin a magnetic brush development arrangement, the toner clings to thecarrier by triboelectric attraction. The carrier particles acquire acharge of one polarity and the toner acquires a charge of the oppositepolarity. Thus, if the carrier is mixed with a resin toner which ishigher in the triboelectric series, the toner normally acquires apositive charge and the carrier a negative charge.

Useful toner granules can be prepared by various methods. Two convenienttechniques for preparing these toners are spray-drying or melt-blendingfollowed by grinding. Spraydrying involves dissolving the resin,colorant and any additives in a volatile organic solvent such asdichloromethane. This solution is then sprayed through an atomizingnozzle using a substantially nonreactive gas such as nitrogen as theatomizing agent. During atomization, the volatile solvent evaporatesfrom the airborne droplets, producing toner particles of the uniformlycolored resin. The ultimate particle size is determined by varying thesize of the atomizing nozzle and the pressure of the gaseous atomizingagent. conventionally, particles of a diameter between about Vapandabout 25p. are used, with particles between about 2p. and 15p, beingpreferred, although larger or smaller particles can be used wheredesired for particular development or image considerations.

Suitable toners can also be prepared by melt-blending. This techniqueinvolves melting a powdered form of polymer or resin and mixing itsuitable colorants and additives. The resin can readily be melted orheated on compounding rolls which are also useful to mix or otherwiseblend the resin and addenda so as to promote the complete intermixing ofthese various ingredients. After thorough blending, the mixture iscooled and solidified. The resultant solid mass is then broken intosmall pieces and finely ground to form a free-flowing powder of tonergranules. The resultant toner granules usually range in size from about9% to about 25 1..

, The resin material used in preparing the toner can be selected from awide variety of materials, including natural resins, modified naturalresins and synthetic resins. Exemplary of useful natural resins arebalsam resins, colophony, and shellac. Exemplary of suitable modifiednatural resins are colophony-modified phenol resins and other resinslisted below with a large proportion of colophony. Suitable syntheticresins are all synthetic resins known to be useful for toner purposes,for example, polymers, such as vinyl polymers and copolymers includingpolyvinyl chloride, polyvinylidene chloride, polyvinyl acetate,polyvinyl acetals, polyvinyl ether, polyacrylic and polymethacrylicesters, polystyrene, including substituted polystyrenes;polycondensates, e.g., polyesters, such as phthalate, terephthali'c andisophthalic polyesters, maleinate resins and colophony-mixed esters ofhigher alcohols; phenol-formaldehyde resins, including modifiedphenol-fonnaldehyde condensates; aldehyde resins; ketone resins;polyamides; polyurethanes, etc. Moreover, chlorinated rubber andpolyolefins, such as various polyethylenes, polypropylenes,polyisobutylenes, are also suitable. Additional toner materials whichare useful are disclosed in the following U.S. Pat. Nos: 2,917,460, Re25,136; 2,788,288; 2,638,416; 2,618,552 and 2,659,670.

The coloring material additives useful in suitable toners are preferablydyestuffs and colored pigments. These materials serve to color the tonerand thus render it more visible. In addition, they sometimes affect, ina known manner the polarity of the toner. In principle, virtually all ofthe compounds mentioned in the Color Index, Vol. I and 11, SecondEdition, 1956, can be used as colorants. Included among the vast numberof suitable colorants would be such materials as Nigrosin Spirit soluble(CI. 50415), I-Iansa Yellow G (CI. 11680), Chromogen Black ETOO (CI.14645), Rhodamine B (CI. 45170), Solvent Black 3 (C.I. 26150), FuchsineN (CI. 42510), C.l. Basic Blue 9 (Q1. 52015), etc. i

The following examples are included for a further understanding of theinvention and all indications of mesh sizes have reference to the U.S.Standard Sieve Series.

EXAMPLE 1 Nickel-plated spherical iron particles are prepared inaccordance with the electroless plating technique of Example 2 ofcopending Miller application Ser. No. 799,967, filed Feb. 17, 1969, nowabandoned, entitled HIGHLY CONDUCT'IVE CARRIER PARTICLES. These coreparticles have a size such that they will pass through an 80 mesh screenand be retained by a 120 mesh screen and they have a resistance of 5ohms as measured in the standard resistance test. Four grams of thenickeLclad iron particles are placed in an aluminum plate at groundpotential and spread around such that they are contained in an areaapproximately 4.3 cm. X 4.3 cm. The aluminum plate is mounted in aninsulating plastic holder capable of being vibrated so as to maintainthe particles in a fluidized state. A high potential electrode comprisedof a 7% X 7% cm. stainless steel plate is mounted approximately 1 cm.above the aluminum plate. The apparatus is placed a vacuum chamberwhichis evacuated to apressure of about 0.8 mm. of mercury. Helium is thenbled into the apparatus to increase the pressure to about 2.0 mm. ofmercury. Next, the core particles are cleaned by applying a 10 kc. a.c.field sufficient to produce a glow at a current of 90 rnilliamperesacross the electrodes for 5 minutes. The electrical equipment used toproduce this field is comprised of an audio oscillator, a 200 watt audioamplifier and a step up transformer. A 1,000 ohm current limitingresistor is placed in the lead to the high voltage electrode and thevoltage drop across this resistor is recorded and used to calculate thecurrent. The a.c. field is terminated and the chamber is evacuated againto about 0.8 mm. of mercury and gaseous tetrafluoroethylene isintroduced into the chamber to increase the pressure to about 1.3 mm. ofmercury. An electric field is again applied using a current of about 45ma. for a period of IS minutes. During the cleaning and coatingoperations, the particles are continually agitated. The resultingparticles are free-flowing and have a thin, continuous layer ofpolymerized tetrafluoroethylene thereon. No agglomeration of particlesoccurs. As measured in the standard resistance test, the particles havea resistance of greater than 10" ohms. The carrier particles asproduced'above are mixed with 4 percent by weight of an electroscopictoner material comprised of a polystyrene resin containing carbon black.The resultant developer mixture is applied to a handheld magnet to forma magnetic brush. This magnetic brush is then used to develop anelectrostatic latent image carried on an electrophotographic elementcomprising a conducting support having coated-thereon a photoconductivelayer containing an organic photoconductor and a polycarbonate binder.The developed image is transferred electrostatically to a white bondpaper receiving sheet and fixed with heat. The developer gives goodfringing development and good image quality. The

EXAMPLE 2 Four grams of the nickel-clad iron particles of Example 1 areplaced in the apparatus described in Example 1 and cleaned by exposureto glow discharge for 2 minutes using a current of ma. in a heliumatmosphere at a pressure of about 1.5 mm. of mercury. The pressure isreduced to about 0.8 mm. of mercury and acrylonitrile vapor is bled intothe apparatus until the pressure rises to about 1.5 mm. of mercury. Theparticles are vibrated continuously while subjected to glow dischargefor 30 seconds with a current of from 50 to 60 ma. The resultant freeflowing particles have a resistance as measured in the standardresistance test of about 5 X 10 ohms. The resultant carrier particlesare mixed with 4 percent by weight of the toner material of Example 1and used to develop an electrostatic image. A fringe developed imageresults which is of good quality.

EXAMPLE 3 Four grams of nickel-plated spherical iron particles similarto those described in Example 1 and having a particle size such thatthey will pass through a 150 mesh screen and be retained by a 200 meshscreen are exposed to a glow in the apparatus described in Example 1.The glow discharge treatment is conducted in a helium atmosphere at apressure of 1.5 mm. of mercury for 5 minutes at a current of 95 ma. Theparticles are removed from the glow discharge apparatus and measured inthe standard resistance test and found to have a resistance of 150 ohmsas compared to 5 ohms prior to the glow discharge treatment. Thisincrease in resistance of about ohms indicates that apparently somesurface oxidation occurs in the glow discharge treatment. The resultantmaterial is used to form a developer mixture comprising 4 percent byweight of the toner of Example 1. The resultant developer mixture isused to develop an electrostatic image and is found to produce solidarea development. Thus, it appears that the fringing developmentobtained in Examples 1 and 2 cannot be exlimited to iron particles inthat the conductivity of the particles to be coated plays no part in theprocedures of this invention. Consequently, the coating or encapsulationprocedures of this invention can be used on any metallic or nonmetalliccore particle. in addition, as mentioned previously, suitable coatingsmay be applied by any system capable of activating a vaporized monomer,and the term glow discharge treatment is meant to include, for example,direct current, alternating current, electrodeless radio frequency andmicrowave glow discharge, as well as ultraviolet treatment and electronbombardment. Similarly, the materials for coating the core particles mayinclude conventional monomers as well as vaporizable organic andinorganic molecules known to undergo glow discharge polymerization.

As described in the above examples, the core particles are maintained inan agitated state during the cleaning and coatin g procedures. It isdesirable that the particles are maintained in this agitated state so asto insure that each particle receives a continuous coat without causingagglomeration of a plurality of particles. Although the separation ofparticles in the above examples is accomplished by a vibratory motion,it is evident that other methods of keeping the particles apart areequally useful such as fluidization with a gas, mechanical stirring orcascading the particles through the polymerizable vapors, etc,

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

We claim:

1. A developer composition for use in developing electro static chargepatterns comprising a mixture of electroscopic toner material and aparticulate, free-flowing carrier vehicle, said carrier vehiclecomprising individual particles each having a core having coated thereona thin, continuous layer of a glow discharge polymerized material.

2. A developer composition for use in developing electrostatic chargepatterns comprising a mixture of electroscopic toner material and aparticulate, free-flowing carrier vehicle for said toner material, saidcarrier vehicle comprising individual particles each having a core of amagnetically responsive material overcoated with a thin, continuous,film of an electrically insulating glow discharge polymerized material.

3. A developer composition in accordance with claim 1 wherein said corecontains a material selected from the group consisting of iron, nickel,cobalt, and alloys thereof and wherein said carrier vehicle has anelectrical resistance of greater than about 10 ohms.

4. A developer composition for use in developing electrostatic chargepatterns comprising a mixture of electroscopic toner material and aparticulate, free-flowing carrier vehicle for said toner, said carriervehicle comprising individual particles each having a core of amagnetically responsive material overcoated with a thin, continuous,film of an electrically insulating glow discharge polymerized material,said core containing a material selected from the group consisting ofiron, nickel, cobalt, and alloys thereof, said glow dischargepolymerized material being formed from a gaseous polymerizable materialselected from the group consisting of trifluoromonochloroethylene,hexafluoropropylene, tetrafluoroethylene, octafluorobutene-2, vinylfluoride, vinylidene fluoride, hexafluoroacetone, acrylonitrile,styrene, ethylene, vinyl chloride, vinyl ferrocene, carbontetrachloride, hexafluoroethane, methyl methacrylate, divinylbenzene,benzene, naphthalene, anthracene and mixtures thereof.

5. A developer composition as described in claim 3 wherein said film onsaid core is formed of a glow discharge polymerized monomer selectedfrom the group consisting of tetrafluoroethylene, acrylonitrile, andvinylidene fluoride.

6. A developer composition as described in claim 3 wherein said tonermaterial comprises from about I to about K) percent by weight of saidcomposition.

* w it it gg gs UNITED STATES PATENT OFFICE CERTIFICATE OF CO ECTIONPatent No. 3,669,;885 Dated June 13, 1972 Inventr(s) J'ohnF- and. ruceJ.

It is certified that error appears in the above-identified ptentand thatsaid Letters Patent, ere-hereby corrected as shown'belowi In theAbstraot,' line 2, "in" should read "of". Column 8, line 29, "3" Shouldd nun Column 3, line 33 "3" should read Signed and sealed this 26th'dayof December 1972.

(SEAL) Attesf:

EDWARD i hFLwTCI-ERJR. I ROBERT GOTTSCHALK Attesiing Officer ICommissioner of Patents

2. A developer composition for use in developing electrostatic chargepatterns comprising a mixture of electroscopic toner material and aparticulate, free-flowing carrier vehicle for said toner material, saidcarrier vehicle comprising individual particles each having a core of amagnetically responsive material overcoated with a thin, continuous,film of an electrically insulating glow discharge polymerized material.3. A developer composition in accordance with claim 1 wherein said corecontains a material selected from the group consisting of iron, nickel,cobalt, and alloys thereof and wherein said carrier vehicle has anelectrical resistance of greater than about 107 ohms.
 4. A developercomposition for use in developing electrostatic charge patternscomprising a mixture of electroscopic toner material and a particulate,free-flowing carrier vehicle for said toner, said carrier vehiclecomprising individual particles each having a core of a magneticallyresponsive material overcoated with a thin, continuous, film of anelectrically insulating glow discharge polymerized material, said corecontaining a material selected from the group consisting of iron,nickel, cobalt, and alloys thereof, said glow discharge polymerizedmaterial being formed from a gaseous polymerizable material selectedfrom the group consisting of trifluoromonochloroethylene,hexafluoropropylene, tetrafluoroethylene, octafluorobutene-2, vinylfluoride, vinylidene fluoride, hexafluoroacetone, acrylonitrile,styrene, ethylene, vinyl chloride, vinyl ferrocene, carbontetrachloride, hexafluoroethane, methyl methacrylate, divinylbenzene,benzene, naphthalene, anthracene and mixtures thereof.
 5. A developercomposition as described in claim 3 wherein said film on said core isformed of a glow discharge polymerized monomer selected from the groupconsisting of tetrafluoroethylene, acrylonitrile, and vinylidenefluoride.
 6. A developer composition as described in claim 3 whereinsaid toner material comprises from about 1 to about 10 percent by weightof said composition.